1. Technical Field
The present invention is generally directed to back flow preventers and, more particularly, to a device to attach to a sill cock or hydrant to prevent back flow of contaminants into the source of supply.
2. Background Art
When a liquid, such as water, is added to another liquid by means of a hose from a supply source to a delivery area, contamination of the supply source by the delivery area fluid can be a major problem. If the pressure from the delivery area is greater than the supply pressure, back flow will occur from the delivery area to the supply source. Contamination of the supply source will therefore result.
Where water or other uncontaminated supply liquids are used to clean and/or dilute toxic or otherwise dangerous liquids, the possibility of contaminating the liquid supply is a serious problem. This problem exists in industrial environments as well as in agricultural and residential applications when water is used to dilute chemicals or other fluids.
The concept of utilizing back flow preventers to control back flow is not new. Typically, a normally closed valve opens with flow into the inlet and closes when inlet flow ceases, at which time back pressure may occur.
When supply pressure is reduced and flow is stopped, liquid accumulates within the valve and in plumbing upstream from the valve. During cold weather, this trapped liquid may freeze, causing severe damage to the valve and upstream plumbing.
Draining features have been incorporated into check valves, such as A. W. Cash Valve Company Model VB-111, which has a stem extending from the outlet side of the valve which may be pushed to open the valve and allow drainage of the valve and upstream plumbing when a hose is not connected.
This type of manually drained valve relied on an operator to drain the valve, and this method of operation is not always reliable. Self-draining check valves are not new in the art and are shown in the following patent.
Lair U.S. Pat. No. 4,712,575, discloses a self-draining, single valve back flow preventer. When a hose is detached, a spool under spring pressure is permitted to move axially outwardly from the outlet end of the check valve. A valve, housed within the spool, thereby moves axially from its sealing washer, permitting flow and drainage. When the hose is connected, the spool and the valve housed within it are forced axially toward the sealing washer, creating a seal that prevents back flow. Atmosphere vent holes in the check valve housing prevent accumulation of back pressure within the valve. Sufficient water pressure during supply flow with the hose attached overcomes a small spring used to seat the valve and deflects the atmospheric vent sealing washer thereby sealing the atmospheric the vent holes.
If the Lair single check type valve becomes contaminated with foreign material, a particle of the contamination may lodge between the valve and the sealing washer, creating a passage through which back flow may occur.
Waterston U.S. Pat. No. 3,905,382, discloses a check valve with two normally closed spring biased valves, one inside the externally-threaded outlet, and the other located near the inlet. The central portion of the check valve has an externally-threaded vent outlet. When flow occurs, the force from the flow moves the inlet valve axially from its seat toward the outlet and seals the vent. The flow then progresses to the outlet valve where the flow pressure compresses the outlet spring and fluid flows from the check valve. When flow stops and back flow pressure is sufficient to overcome the valve in the outlet, liquid accumulates in the sealed tube and is discharged through the vent outlet.
Waterston does not provide for a draining feature to relieve accumulated liquid upstream from the check valve. The accumulation of liquid upstream from the check valve will result in severe damage to the check valve and plumbing upstream of the check valve in the event of freezing of the liquid. Also, Waterston does not provide for a draining feature for the internal portions of the check valve. Contamination may collect in the internal portion of the check valve when back flow conditions occur and, when normal flow resumes, the contamination trapped in the check valve will flow to the output destination. Further, the contamination within the check valve may cause internal damage through corrosion or severe damage may occur due to freezing if the valve is exposed to subfreezing temperatures.
The above check valves do not adequately assure the prevention of contamination from entering the supply source. If particulate matter is present in the contaminated output liquid, during back flow some of the particulate may become lodged between the valve and the valve seat of the back flow preventer. When this occurs, proper sealing is prevented and contamination may be permitted to enter the supply source.
Supply liquid and contaminates are frequently trapped in the inner workings of back flow preventers. The trapped liquids cause great harm to the back flow preventer when the liquids expand during freezing or if the liquids are corrosive liquids. Also, the trapped contamination can be released later into another delivery area.
Liquid is often trapped upstream of the back flow preventers when the outlet line to the check valve has been disconnected. The trapped liquid expands if frozen and may cause severe damage to the back flow preventer and the supply line.
The present invention is directed toward overcoming one or more of the problems discussed above.